1. Field of the Invention
Our invention is a wireless modulated carrier wave communication system in which a separated transmitter and receiver transmit and receive digital data through the earth.
2. Description of the Prior Art
The transmission of data from one underground station to another station can be found in many references such as those found in class 325, sub-class 28 of the U.S. patent classification definitions. Three examples are U.S. Pat. Nos. 2,389,432, 2,499,195, and 2,992,325 to C. W. Hansell, J. A. McNiven, and F. W. Lehan, respectively. In none of these systems is a FSK system with short tone bursts of short duration used to transmit and receive data. In those systems employing FSK techniques the signals are transmitted on 100 percent of the duty cycle per channel. These types of systems can be found in the U.S. Pat. having Nos. 3,717,844 and 3,924,065 to Barret et al and Charles C. Freeny, respectively. The distinguishing characteristics of our FSK system over these are our shorter cycles with short tone bursts, our receiver alert code, and our noise suppressing network. None of the known prior art has all or most of the features found in our invention.
The unique combination of features present in our invention allows us to operate a long life battery powered telemetry transmitter in a mine which is virtually uneffected by noise transients. To be sure that these signals are accurately received, a receiver alert code is transmitted prior to the actual data.